(a) Field of the Invention
The present invention relates to an automotive automatic transmission, and in particular, to an anti-rollback system and method capable of preventing a vehicle from rolling back when starting on a slope, using an improved magnetic sensor mechanism which detects a rotational direction of an output shaft so as to optimally control the automatic transmission.
(b) Description of the Related Art
FIG. 1 and FIG. 2 show respectively a conventional magnetic sensor mechanism and a graph showing an electromagnetic wave form generated by the magnetic sensor.
The conventional anti-rollback system comprises a magnetic sensor mechanism including an output gear 4 mounted on an output shaft 2 of an automatic transmission (not shown) and a magnetic sensor 8 for detecting output torque by sensing magnetic teeth 6 formed on the output gear 4, signals detected by the magnetic sensor 8 being parameters for an ECU (electronic control unit) 10 to control vehicle speed.
If the magnetic sensor 8 detects a rotation of the output shaft 2, an electromagnetic wave shows a waveform similar to that shown in FIG. 2 such that the ECU 10 controls parts of a vehicle on the basis of this signal.
However, when a vehicle equipped with this magnetic sensor mechanism starts after a stop on an uphill slope, the vehicle may roll back a little before moving forward, which startles a driver and may cause a minor collision. This is because the ECU can not distinguish the rotational directions of the output shaft on the basis of the signal having a monotonous waveform from the magnetic sensor.
Furthermore, since an engine rpm (revolutions per minute) must be up to prevent the vehicle from rolling back on slope-starting, the idle rpm causes both fuel to be wasted and vibration noise. In addition, the increased rpm causes acceleration shocks to be aggravated on a downhill slope.
The present invention has been made in an effort to solve the above problems of the prior art.
It is an object of the present invention to provide an anti-rollback mechanism capable of preventing a vehicle from rolling back on an uphill slope using an improved magnetic sensor mechanism which distinguishes rotational directions of an output shaft of an automatic transmission.
To achieve the above object, an anti-rollback system for an automatic transmission comprises an output gear connected to an output shaft of the automatic transmission, and a magnetic sensor for detecting output rpm of the output gear, the magnetic sensor being electrically connected to an ECU (electronic control unit), wherein the output gear has a plurality of teeth, each tooth having a slot formed on an upper surface thereof.